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  1. #include <bits/stdc++.h>
  2. using namespace std;
  3. typedef long long ll;
  4. const int Mod=998244353;
  5. const ll INF = -10000000000000;
  6.  
  7. void solve() {
  8.     int n;
  9.     cin >> n;
  10.     vector<ll> a(n+1);
  11.     for(int i = 1; i <= n; i++) cin >> a[i];
  12.  
  13.     unordered_map<ll, vector<ll>> mp;
  14.     for(int i = 2; i <= n; i++){
  15.         ll need = a[i] + i - 1;
  16.         ll gain = i - 1;
  17.         mp[need].push_back(need + gain);
  18.     }
  19.  
  20.     ll best = n;
  21.     unordered_set<ll> seen;
  22.     queue<ll> q;
  23.     q.push(n);
  24.     seen.insert(n);
  25.  
  26.     while(!q.empty()){
  27.         ll L = q.front(); 
  28.         q.pop();
  29.         best = max(best, L);
  30.  
  31.         auto it = mp.find(L);
  32.         if(it == mp.end()) continue;
  33.  
  34.         for(ll nxt : it->second){
  35.             if(seen.insert(nxt).second){
  36.                 q.push(nxt);
  37.             }
  38.         }
  39.         mp.erase(it);
  40.     }
  41.  
  42.     cout << best << "\n";
  43. }
  44.  
  45. int main(){ 
  46.     ios::sync_with_stdio(false);
  47.     cin.tie(nullptr);
  48.  
  49.     int t;
  50.     cin >> t;
  51.     while (t--) solve();
  52.  
  53.  
  54.     return 0;
  55. }
  56.  
Success #stdin #stdout 0.01s 5296KB
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https://ideone.com/4F2QCk
language:
C++ (gcc 8.3)
created:
11 days ago
visibility:
public

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